Hypolchlorite-chlorite bleaching of soapstock



United States HYPOCHLORITE-CHLORITE BLEACHING F SOAPSTOCK No Drawing. Application January 13, 1955, Serial No. 481,709

Claims priority, application Great Britain February 16, 1954 2 Claims. (Cl. 260-419) This invention relates to the treatment of soapstock and in particular to the treatment of soapstock to obtain good colored soaps therefrom.

Vegetable and animal oils as extracted from plant or animal tissue usually contain free fatty acids and are usually treated with an aqueous alkali such as caustic soda to remove such free fatty acids when it is desired to use the oil for edible purposes. The treatment with alkali results in a refined oil and an aqueous phase, usually referred to as soapstock. In addition to the soap resulting from the reaction between the free fatty acids and alkali, this soapstock contains, in a concentrated form, dirt or coloring matter previously present in the unrefined o l, together with a considerable quantity of occluded neutral oil.

If such soapstock is added to charges of oil to be saponified in a soap making process, the resulting soap from such charges is of poor color due to high concentrations of dirt and coloring matter present in the soapstock. If a soap of good color is desired it is possible to bleach the oil mixture from which the soap is to be obtained with a bleaching earth. Alternatively, instead of being added to a soap charge, the soapstock may be treated with a mineral acid such as sulfuric acid to release the fatty acids from the soap. After separation of the aqueous phase, a mixture consisting of the released fatty acids and the occluded neutral oil is obtained. As the proportion of fatty acids in this mixture is considerably higher than in the original unrefined oil, it is usual to refer to this oil as acid oil. This splitting of soapstocks may be a costly and laborious operation.

Such acid oil, that is oil containing a high proportion of fatty acids, will also contain a proportion of the dirt and undesirable coloring matter present in the original oil. Like the soapstock, it is sometimes added to the charges of oil used in soap making. The resulting soap from such a charge is also of poor color. Hence, if it is desired to produce a soap of good color, the original oil and the acid oil from the soapstock or an oil blend containing this acid oil has to be bleached with a bleaching earth.

The bleaching by means of bleaching earth of oils containing free fatty acids such as the above described acid oils or blends of oil containing such acid oil is a laborious and costly process involving filtering of the oil from the earth. It also involves a treatment of the spent earth to recover the considerable amount of oil which is adsorbed by the earth during the treatment. Consequently, earth bleaching of oils is adopted in the soap making industry only when it is desired to produce soaps of the very highest quality, for example, toilet soaps.

In view of the above disadvantages of earth bleaching and also the splitting of soapstocks into acid oils, attempts have been made to chemically bleach either the soapstock as such, or soap obtained by saponifying a charge of oil containing such soapstock. Hypochlorites, such as sodium hypochlorite, have been tried both for bleaching soapstocks and the soaps obtained by saponifying 153 iiiitttttltibt:

atent O 2,810,735 Patented Oct. 22, 1957 charges of oils containing soapstock. Such hypochlorites are not effective in bleaching soapstock nor soaps obtained by saponifying oil charges containing soapstocks unless suitable agitation is employed. Also, unless suitable agitation is employed, the soap or soapstock tends to revert to its unbleached color on standing. The degree of agitation with hypochlorite has to be such that hypochlorite treatment is not readily carried out batchwise.

It is an object of the present invention to provide a process of bleaching soapstocks obtained in the alkalirefining of animal and vegetable oils with an alkali metal hypochlorite, such as sodium or potassium hypochlorite, which avoids the above mentioned disadvantages.

The present invention provides a process of bleaching soapstocks obtained in the alkali-refining of animal and vegetable oils which process comprises contacting the soapstock with a hypochlorite in the presence of an alkali metal chlorite.

The hypochlorite and chlorite, which are preferably sodium salts, may both be used in the form of their aqueous solutions. If desired, however, the hypochlorite may be formed in situ in the mixture under treatment; for example, when the hypochlorite is sodium hypochlorite, by adding sodium hydroxide to the soapstock and passing chlorine gas through it. The chlorite might also be formed in situ by passing a suitably diluted chlorine dioxide gaseous mixture into soapstock containing an alkali.

The amount of chlorite used is preferably between 0.1% and 10% and the amount of aqueous hypochlorite, containing about 14% available chlorine, is preferably between 0.1% and 20%, i. e., from about 0.02 to 3% hypochlorite, expressed as alkali metal hypochlorite, all figures being based on the total weight of soapstock. For best results, the amount of chlorite is 0.5%.

The chlorite may be added to the soapstock before, with or after the hypochlorite. Preferably the chlorite and hypochlorite solutions are mixed immediately prior to the addition to the soapstock.

The temperature of the soapstock should be between 40 C. and C. and is preferably about 60 C., while the time of contact with the chlorite and hypochlorite is preferably between about 0.5 minutes and 30 minutes. When carrying out the treatment batchwise optimum results are obtained when the time of contact is about 15 minutes.

The fact that the time of contact can be relatively short is advantageous in that it enables a stream of soapstock and a stream of hypochlorite-chlorite to be passed into a convenient form of mixing device, such as a centrifugal pump, from which a substantially bleached soapstock will issue without having been violently agitated. This means that the process of the invention can be used to supply directly to the saponification stage of a continuous soap making process a stream of bleached soapstock and removes any limitation on the amount of soapstock which may be used in such a continuous soap making process.

It is preferred to contact the soapstock with the chlorite and hypochlorite in a chemically-resistant vessel as the resultant mixture may attack non-resistant materials and this may result in less efficient decolorization of the soapstock than would otherwise be obtained.

This invention has the advantage that it permits the resultant soapstock to be used directly in the manufacture of good colored soaps, thereby avoiding the necessity of submitting them to the above described splitting with mineral acid to produce acid oils. The fact that the soapstock which contains in a concentrated form all the impurities originally present in the unrefined oil can be bleached to give a soapstock of good color and ultimately be used in conjunction with the normal oil blends for the production of good colored soaps, and that both DEl-liibii HUUi i the color of the soapstock and soap does not show any great tendency to revert is surprising, especially when it is remembered that no violent agitation need be employed in the process of the present invention. The agitation need be sufficient only to insure uniform dispersion of the soapstock with the chlorite and hypochlorite.

The invention will now be illustrated by means of the following examples. In these examples the Lovibond color unit readings were obtained by converting a sample of the oil-soap mixture under examination to the fully saponified soap and dissolving this soap in 70% by volume ethyl alcohol to obtain a 10% by weight alcoholic soap solution of which Lovibond color measurements were then made in a 2 inch cell. Parts are by weight.

EXAMPLE 1 One hundred (100) parts of palm oil soapstock containing from 40 to 50% total fatty matter and having a soap to oil ratio of 1.5:1 are heated to 60 C. in a glass or other chemically-resistant vessel fitted with a mechanical agitator. 0.5 part of sodium chlorite dissolved in water to form a 50% solution are mixed with parts of aqueous sodium hypochlorite having an available chlorine content of 14%. The mixture is added to the soapstock immediately after formation, the soapstock being stirred continually during the addition. The mixture is agitated for 15 minutes at 60 C. before being saponified into a fully saponified soap.

Lovibond color measurements on a alcoholic soap solution were made in a 2 inch glass cell and are given in the following Table I, which also gives Lovibond measurements on alcoholic soap solutions made up from soaps obtained by fully saponifying respectively untreated palm oil soapstock, soapstock treated with a 5.0% by weight aqueous hypochlorite liquor and soapstock obtained from oils previously bleached with 7% by weight of bleaching earth.

Table I Lovibond Readings on Alcoholic Origin of Soap Soap Solutions Yellow Red Untreated soapstock from red palm oil 31.0 5. 4 Soapstock treated with 5% hypochlorite liquor. 30.0 3. 4 Soapstock from earth bleached red palm oil 7.0 1. 9 Soapstock treated with a 0.5% chlorite and 5 0% hypochlorite liquor 4. 0 0. 9

It is clear that soaps from red palm oil soapstock treated according to the present invention are much lighter in color than soaps from the unbleached soapstock or hypochlorite bleached soapstock or soapstock from earth bleached oils.

EXAMPLE 2 Similar experiments to those given under Example 1 were carried out on peanut oil soapstock instead of red palm oil soapstock, except that the time of treatment was The table shows that the conclusion reached in Example l in the case of red palm oil soapstock also applies in the case of peanut oil soapstock.

EXAMPLE 3 Similar experiments to those of Example 2 carried out with rapeseed oil soapstock gave the results in the following table:

This example illustrates the formation of the hypochlorite in situ. One hundred parts of red palm oil soapstock used in Example 1 are heated to 60 C. as described in Example 1. 0.5 parts of sodium chlorite dissolved in suflicient water to form a 50% solution are added to the soapstock, the soapstock being agitated during the addition. The mixture is kept at 60 C. while rsufiicient sodium hydroxide solution is added to give, after reaction with chlorine gas, the equivalent of a liquor containing 5% sodium hypochlorite based on the weight of the soapstock. The resultant mixture is passed through any enclosed mixing device of chemically-resistant imaterial, such as a centrifugal pump. The necessary amount of chlorine gas to form with the sodium hydroxide in the mixture the equivalent of a 5% sodium hypochlorite mixture is fed into the mixing apparatus, for example, into the inlet side of the centrifugal pump. The bleached soapstock passing continuously out of the mixing apparatus is converted into a fully saponified soap and Lovibond readings are taken in the manner already described on samples of this soap. The following table illustrates the results of this experiment in comparison with the results of the similar Lovibond readings on soaps from red palm oil soapstock treated with 5% sodium hypochlorite liquor and untreated red palm oil soapstock:

EXAMPLE 5 This example illustrates the addition of the hypochlorite after the chlorite. In this example 100 parts of red palm oil soapstock are treated at 60 C. With 0.5 parts of sodium chlorite added in the form of a 50% aqueous solution in a reaction vessel such as is mentioned in Example 1 and fitted with mechanical agitation. After the chlorite has been well mixed with the soapstock, 5 parts of sodium hypochlorite liquor containing approximately 14% by weight of available chlorine are added while the reaction mixture is being agitated. Agitation is continued as in Example 1 and then fully saponified soap is prepared from the mixture by saponification. Lovibond measurements on an alcoholic solution of the resultant soap are carried out as well as on alcoholic solutions of soaps from untreated soapstock and of soaps from soapstock treated with sodium hypochlorite liquor.

The results obtained are given in the following table:

EXAMPLE 6 This example illustrates the short time of contact required when treating soapstock according to the present invention. In this example 100 parts of palm oil soapstock containing 30 parts of soap and 40 parts of palm oil were heated to between 60 and 65 C. in a glass or other chemically-resistant vessel fitted with a mechanical agitator. 0.5 parts of sodium chlorite dissolved in water to form a 50% solution were mixed with 5 parts of sodium hypochlorite liquor having an available chlorine content of 14%. Immediately after this mixture had been made it was added to the soapstock which was continuously agitated. Samples were withdrawn from the reaction vessel at intervals of time shown in Table 6 below. These samples were examined for color to test the speed of the bleaching reaction. The colors of the samples were measured in Lovibond units in a 2 inch cell on a solution of the soapstock in a 1:1 mixture of ethyl alcohol and chloroform. An analogous series of results were also obtained by treating soapstock alone with hypochlorite. The results with hypochlorite are also given in the following table:

This table clearly shows that the reaction between soapstock and a hypochlorite/chlorite mixture is extremely rapid and that considerable bleaching takes place within 15 seconds. Hypochlorite alone under the same conditions shows no bleaching action within a similar period of time.

The soapstock treated according to the invention may be derived from any animal or vegetable oil. Examples of such oils are peanut oil, palm oil, rapeseed oil, coconut oil, cotton seed oil, soybean oil, fish oil and like oils.

I claim:

1. A process of bleaching soapstock which comprises contacting soapstock, in indiflerent order, with an alkali metal hyprochlorite and an alkali metal chlorite in aqueous solution at a temperature from about 40 to C., the amount of chlorite being from about 0.1 to 10% by weight of the soapstock and the amount of hypochlorite, expressed as alkali metal hypochlorite, being from about 0.02 to 3% by weight of the soapstock.

2. The process of claim 1 in which the chlorite is sodium chlorite and the hypochlorite is sodium hypochlorite.

References Cited in the file of this patent UNITED STATES PATENTS 104,470 Loew June 21, 1870 301,783 Wilson July 8, 1884 2,235,837 Logan Mar. 25, 1941 2,269,667 Kauffmann Ian. 13, 1942 2,430,675 Hampel Nov. 11, 1947 2,433,662 Hampel Dec. 30, 1947 2,481,463 Woodward et al. Sept. 6, 1949 2,662,884 Jenkins Dec. 15, 1953 

1. A PROCESS OF BLEACHING SOAPSTOCK WHICH COMPRISES CONTACTING SOAPSTOCK, IN INDIFFERENT ORDER, WITH AN ALKALI METAL HYPROCHLORITE AND AN ALKALI METAL CHLORITE IN AQUEOUS SOLUTION AT A TEMPERATURE FROM ABOUT 40 TO 100*C., THE AMOUNT OF CHLORITE BEING FROM ABOUT 0.1 TO 10% BY WEIGHT OF THE SOAPSTOCK AND THE AMOUNT OF HYDROCHLORITE, EXPRESSED AS ALKALI METAL HYPOCHLORITE, BEING FROM ABOUT 0,02 TO 3% BY WEIGHT OF THE SOAPSTOCK. 